1. Field of the Invention
The present invention relates to a method of fusion-splicing polarization maintaining optical fibers.
2. Description of the Related Art
As shown in FIGS. 1A to 1C, polarization maintaining optical fiber 14 has core 16 at its center and a pair of stress applying members 18 at both sides of the core. This type of fiber is generally called a "PANDA" type fiber. In order to fusion-splice two such fibers 14, alignment of fibers 14 is performed such that the direction which is perpendicular to the axes of the stress applying members 18 of one of the optical fibers is so arranged as follows with respect to the direction which is perpendicular to the axes of the stress applying members 18 of the other of the optical fibers. That is, as shown in FIG. 1A, the two directions are the same each other; as shown in FIG. 1B, one direction is shifted from the other through 90.degree.; and as shown in FIG. 1C, one direction is shifted from the other through 45.degree.. For this purpose, in addition to alignment in the x and y directions and adjustment of an interval between fiber ends in the z direction, alignment in the circumferential direction, i.e., the .theta. direction must be performed.
FIGS. 2A and 2B show an apparatus (Japanese Patent Application No. 61-115901) for fusion-splicing a pair of polarization maintaining optical fibers.
In FIGS. 2A and 2B, reference numerals 10 denote polarization maintaining optical fibers; 12, jacketed fiber portions; and 14, exposed fiber portions.
Reference numerals 20 denote V-groove blocks capable of moving in the x and y directions. Each fiber 14 is placed on block 20 and clamped by fiber clamp 22.
Reference numerals 24 denote z-axis tables. Each jacketed portion 12 is placed on table 24 and clamped by jacket clamp 26. Each table 24 can be pivoted about pin 28 in the direction of arrow 30 so that the upper surface of table 24 moves in the z direction.
Reference numerals 32 denote brackets for rotatably supporting cylindrical members 34A and 34B. In FIG. 2A, dial 36 is directly connected to member 34A.
Two arms 38 (only one is shown in FIG. 2A; see FIG. 2B) project from each of members 34A and 34B, and .theta.-clamps 40 are formed at their distal ends.
Each clamp 40 has V-groove 42 (FIG. 2B). When two arms 38 are moved close to each other, jacketed portion 12 is moved on guide plate 44 and received in V-grooves 42.
In this state, by rotating dial 36 connected to cylindrical member 34A, fiber 10 is rotated in its circumferential direction, i.e., the .theta. direction.
Gear 46 is directly connected to cylindrical member 34B and rotated by motor 48.
Table 24 and bracket 32 are mounted on a single block (not shown) capable of moving in the z-axis direction by use of a motor.
Reference numeral 50 denotes a striking rod or spacer; 52, mirrors mounted on both sides of the upper end of rod 50; and 54, a microscope.
An operation of the apparatus having the above arrangement is as follows.
(1) Fibers 10 are set in the apparatus and clamped by fiber clamps 22, jacket clamps 26 and .theta.-clamps 40.
(2) An initial interval between end faces of fibers 10 to be fused is set.
For this purpose, rod 50 is used. That is, rod 50 is moved upward to its upper limit, and fibers 10 are moved forward in z direction until their end faces to be fused abut against the side surfaces of rod 50.
(3) Rod 50 is moved downward, and preliminary discharge (fire polish) is performed to clean the end faces and to form slight recess portions in stress applying members.
(4) Coarse alignment in the .theta. direction is performed.
That is, rod 50 is moved upward again to an intermediate position, and while observing through microscope 54 end face images of fibers 10 reflected by mirrors 52, dial 36 is rotated so that the positions of stress applying members 18 of the pair of fibers satisfy the predetermined relationship shown in FIGS. 1A, 1B or 1C.
(5) Alignment in the x and y directions is performed.
(6) Fine alignment in the .theta. direction is performed.
In order to perform alignment in the .theta. direction, clamps 26 are released so that fibers 10 can be rotated without any resistance.
(7) Alignment in the x and y directions is performed again (because an axis of the core is offset by .theta. alignment if the core is off-centered).
(8) The fibers are fusion-spliced with each other.
The above core aligning operations of (5) to (7) are performed by what is known as a remote injection and detection system.
In the above method and apparatus, however, three types of clamps 22, 26 and 40 must be used to clamp one fiber. Therefore, the following problems arise:
(1) Since clamps 22 and 40 are located far apart, fiber 10 can easily become twisted while it is rotated in the .theta. direction.
For this reason, very fine adjustment must be performed in order to achieve precise alignment in the .theta. direction.
(2) Because of the long distance between clamps 22 and 40, jacketed portion 12 is bent while x-axis table 24 moves in the z direction. Therefore, the distal end of fiber 10 cannot follow the z direction operation.
For this reason, fiber 10 moves forward/backward in the z direction upon alignment in the .theta. direction, or fiber 10 is not moved in a predetermined manner by the z-direction moving operation upon fusing, resulting in an unstable splicing state.
(3) A mechanism is required to release jacket clamp 26 upon .theta. rotation of fiber 10, the operation of the mechanism is troublesome.